Integrated oxygenate conversion and product cracking

ABSTRACT

Improved processing of an oxygenate-containing feedstock for increased production or yield of light olefins. Such processing involves oxygenate conversion to olefins and subsequent cracking of heavier olefins wherein at least a portion of the products from each of the reactors is elevated in pressure, using a common compressor, prior to being routed to a common product fractionation and recovery section. In one particular embodiment, the cracked product gas can be treated to remove acid gas therefrom. In another embodiment, the olefin cracking reactor is a moving bed reactor.

BACKGROUND OF THE INVENTION

This invention relates generally to the conversion of oxygenates toolefins and, more particularly, to light olefins.

Light olefins serve as feed materials for the production of numerouschemicals. Light olefins have traditionally been produced through theprocesses of steam or catalytic cracking. The limited availability andhigh cost of petroleum sources, however, has resulted in a significantincrease in the cost of producing light olefins from such petroleumsources.

The search for alternative materials for light olefin production has ledto the use of oxygenates such as alcohols and, more particularly, to theuse of methanol, ethanol, and higher alcohols or their derivatives.Molecular sieves such as microporous crystalline zeolite andnon-zeolitic catalysts, particularly silicoaluminophosphates (SAPO), areknown to promote the conversion of oxygenates to hydrocarbon mixtures,particularly hydrocarbon mixtures composed largely of light olefins.

The amounts of light olefins resulting from such processing can befurther increased by reacting, i.e., cracking, heavier hydrocarbonproducts, particularly heavier olefins such as C₄ and C₅ olefins, tolight olefins. For example, commonly assigned, U.S. Pat. No. 5,914,433to Marker, the entire disclosure of which is incorporated herein byreference, discloses a process for the production of light olefinscomprising olefins having from 2 to 4 carbon atoms per molecule from anoxygenate feedstock. The process comprises passing the oxygenatefeedstock to an oxygenate conversion zone containing a metalaluminophosphate catalyst to produce a light olefin stream. A propyleneand/or mixed butylene stream is fractionated from said light olefinstream and cracked to enhance the yield of ethylene and propyleneproducts. This combination of light olefin product and propylene andbutylene cracking in a riser cracking zone or a separate cracking zoneprovides flexibility to the process which overcomes the equilibriumlimitations of the aluminophosphate catalyst. In addition, the inventionprovides the advantage of extended catalyst life and greater catalyststability in the oxygenate conversion zone.

Mechanical devices are used for driving fluids to appropriate locationsat desired pressures. A pump is a mechanical device or machine that isused to force a liquid phase material from one pressure to a higherpressure. The mechanical work performed by a pump is proportional to thevolume of the liquid being pumped times the differential pressure whichis outlet pressure minus inlet pressure. Some of the mechanical work isexpended in transferring the liquid from one location to another. Pumpsare not typically sufficiently powerful to change the volume of theliquid being pumped. A compressor is a mechanical device or machine thatis used to force a vapor phase material from one pressure to a higherpressure. The mechanical work performed by a compressor is proportionalto the volume of the vapor being pumped times the differential pressure.Compressors typically decrease the volume of the vapor being pumped.Material in the liquid phase is always much more dense than material inthe vapor phase. For the same mass of material, the work required topump liquid is always much less than the work required to pump vapor viacompressor.

Further improvements such as relating to reducing or minimizing systemprocessing costs and complexity, however, are desired and are beingsought.

In view thereof, there is a need and a demand for improved processingand systems for the conversion of oxygenates to olefins and, moreparticularly, for such processing and systems such as to result in anincrease in the relative amount of light olefins.

SUMMARY OF THE INVENTION

A general object of the invention is to provide or result in improvedprocessing of an oxygenate-containing feedstock to light olefins.

A more specific objective of the invention is to overcome one or more ofthe problems described above.

The general object of the invention can be attained, at least in part,through a process for producing light olefins from anoxygenate-containing feedstock. In accordance with one preferredembodiment, such a process involves contacting the oxygenate-containingfeedstock in an oxygenate conversion reactor with an oxygenateconversion catalyst and at reaction conditions effective to convert theoxygenate-containing feedstock to an oxygenate conversion product streamcomprising fuel gas hydrocarbons, light olefins, and C₄₊ hydrocarbons.At least a portion of the oxygenate conversion product stream issubsequently compressed via a first compressor. The compressed oxygenateconversion product stream is treated in a gas concentration system torecover light olefins and to form a C₄₊ hydrocarbon stream. At least aportion of the C₄₊ hydrocarbon stream is contacted in an olefin crackingreactor with an olefin cracking catalyst and at reaction conditionseffective to convert C₄ and C₅ olefins therein contained to a crackedolefins effluent stream comprising light olefins. At least a portion ofthe cracked olefins effluent stream is returned to the first compressorfor combination with the oxygenate conversion product stream andsubsequent treatment in the gas concentration system.

The prior art generally fails to provide processing of oxygenates toolefins, particularly such as to result in an increase in the relativeamount of light olefins, and which processing is one or more as simple,effective, as economic as may be desired.

In another embodiment, there is provided a process for producing lightolefins from a methanol-containing feedstock. The process involvescontacting the methanol-containing feedstock in a methanol conversionreactor fluidized reaction zone with a methanol conversion catalyst andat reaction conditions effective to convert the methanol-containingfeedstock to a methanol conversion product stream comprising fuel gashydrocarbons, light olefins, and C₄₊ hydrocarbons. At least a portion ofthe methanol conversion product stream is subsequently compressed via afirst compressor. The compressed methanol conversion product stream ittreated in a gas concentration system to recover light olefins and toform a fuel gas hydrocarbon stream and a C₄₊ hydrocarbon stream. The C₄₊hydrocarbon stream is fractionated to form a process stream comprisingC₄₊ through C⁶⁻ hydrocarbons and a purge stream comprising C₇₊hydrocarbons. The process stream is contacted in an olefin crackingreactor with an olefin cracking catalyst and at reaction conditionseffective to convert C₄ and C₅ olefins therein contained to a crackedolefins effluent stream comprising light olefins. The cracked olefinseffluent stream is separated into a first stream comprising C₁ and C₂hydrocarbons and a second stream comprising a remainder of the olefincracking product stream. The first stream is returned to the firstcompressor for combination with the oxygenate conversion product streamand subsequent treatment in the gas concentration system and the secondstream is introduced to the gas concentration system withoutcompression.

There is also provided a system for converting oxygenates to lightolefins. In accordance with one embodiment, a reactor is provided forcontacting an oxygenate-containing feedstream with catalyst andconverting the oxygenate-containing feedstream to an oxygenateconversion product stream comprising fuel gas hydrocarbons, lightolefins, and C₄₊ hydrocarbons. A first compressor is provided tocompress at least a portion of the oxygenate conversion product streamto form a compressed oxygenate conversion product stream. A gasconcentration system is provided to treat the compressed oxygenateconversion product stream to recover light olefins and to form a C₄₊hydrocarbon stream. The system further includes a reactor for contactingat least a portion of the C₄₊ hydrocarbon stream with catalyst andconverting C₄ and C₅ olefins therein contained to a cracked olefineffluent stream comprising light olefins. A first return line isprovided wherein at least a portion of the cracked olefin effluentstream is introduced into the first compressor and subsequentlyprocessed through the gas concentration system.

As used herein, references to “light olefins” are to be understood togenerally refer to C₂ and C₃ olefins, i.e., ethylene and propylene.

Other objects and advantages will be apparent to those skilled in theart from the following detailed description taken in conjunction withthe appended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic diagram of a process for the conversionof an oxygenate-containing feedstock to olefins in accordance with oneembodiment.

FIG. 2 is a simplified schematic diagram of a process for the conversionof an oxygenate-containing feedstock to olefins in accordance withanother embodiment.

FIG. 3 is a simplified schematic diagram of a process for the conversionof an oxygenate-containing feedstock to olefins in accordance with yetanother embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Oxygenate-containing feedstock can be converted to light olefins in acatalytic reaction and heavier hydrocarbons (e.g., C₄₊ hydrocarbons)formed during such processing can be subsequently cracked to increasethe light olefins (e.g., C₂ and C₃ olefins) produced or resultingtherefrom. In accordance with a preferred embodiment, at least a portionof the oxygenate conversion product stream and at least a portion of theolefin cracking product stream are elevated in pressure, together orseparately, through the same compressor prior to being routed through anappropriate gas concentration system.

FIG. 1 schematically illustrates a system, generally designated by thereference numeral 10, for the conversion of an oxygenate-containingfeedstock to olefins in accordance with one embodiment.

More particularly, an oxygenate-containing feedstock 12 such asgenerally composed of light oxygenates such as one or more of methanol,ethanol, dimethyl ether, diethyl ether, or mixtures thereof, isintroduced into an oxygenate conversion reactor section 14 wherein theoxygenate-containing feedstock contacts with an oxygenate conversioncatalyst at reaction conditions effective to convert theoxygenate-containing feedstock to an oxygenate conversion product streamcomprising fuel gas hydrocarbons, light olefins, and C₄₊ hydrocarbons,in a manner as is known in the art, such as, for example, utilizing afluidized bed reactor.

As will be appreciated by those skilled in the art and guided by theteachings herein provided, such a feedstock may be commercial grademethanol, crude methanol or any combination thereof. Crude methanol maybe an unrefined product from a methanol synthesis unit. Those skilled inthat art and guided by the teachings herein provided will understand andappreciate that in the interest of factors such as improved catalyststability, embodiments utilizing higher purity methanol feeds may bepreferred. Thus, suitable feeds may comprise methanol or a methanol andwater blend, with possible such feeds having a methanol content ofbetween about 65% and about 100% by weight, preferably a methanolcontent of between about 80% and about 100% by weight and, in accordanceone preferred embodiment, a methanol content of between about 95% andabout 100% by weight

A methanol-to-olefin unit designed to process about 2,500,000 metrictons per year of 95 wt. % methanol may have a feed rate of preferablybetween about 1500 and about 4000 kMTA and more preferably between about2000 and about 3500 kMTA. The feedstream may comprise between about 0and about 35 wt. % and more preferably between about 5 and about 30 wt.% water. The methanol in the feed stream may comprise between about 70and about 100 wt. % and more preferably between about 75 and about 95wt. % of the feedstream. The ethanol in the feedstream may comprisebetween about 0.01 and about 0.5 wt. % and more typically between about0.1 and about 0.2 wt. % of the feedstream although higher concentrationsmay be beneficial. When methanol is the primary component in thefeedstream, the higher alcohols in the feedstream may comprise betweenabout 200 and about 2000 wppm and more typically between about 500 andabout 1500 wppm. Additionally, when methanol is the primary component inthe feedstream, dimethyl ether in the feedstream may comprise betweenabout 100 and about 20,000 wppm and more typically between about 200 andabout 10,000 wppm.

Reaction conditions for the conversion of oxygenates to light olefinsare known to those skilled in the art. Preferably, in accordance withparticular embodiments, reaction conditions comprise a temperaturebetween about 200° and about 700° C., more preferably between about 300°and 600° C., and most preferably between about 400° and about 550° C. Aswill be appreciated by those skilled in the art and guided by theteachings herein provided, the reactions conditions are generallyvariable such as dependent on the desired products. For example, ifincreased ethylene production is desired, then operation at a reactortemperature between about 475° and about 550° C. and more preferablybetween about 500° and about 520° C., may be preferred. If increasedpropylene production is desired, then operation at a reactor temperaturebetween about 350° and about 475° C. and more preferably between about400° and about 430° C. may be preferred. The light olefins produced canhave a ratio of ethylene to propylene of between about 0.5 and about 2.0and preferably between about 0.75 and about 1.25. If a higher ratio ofethylene to propylene is desired, then the reaction temperature ishigher than if a lower ratio of ethylene to propylene is desired. Thepreferred feed temperature range is between about 120° and about 210° C.More preferably the feed temperature range is between about 180° and210° C. In accordance with one preferred embodiment, the temperature isdesirably maintained below 210° C. to avoid or minimize thermaldecomposition.

The oxygenate conversion reactor section 14 produces or results in anoxygenate conversion product or effluent stream 16 generally comprisingfuel gas hydrocarbons, light olefins, and C₄₊ hydrocarbons. Theoxygenate conversion reactor section 14 may also, as shown, produce orresult in a wastewater stream 20, such as, for example, may contain lowlevels of unreacted alcohols as well as small amounts of oxygenatedbyproducts such as low molecular weight aldehydes and organic acids, andsuch as may be appropriately treated and disposed or recycled.

The oxygenate conversion product stream 16 and a recycle stream 22, suchas described in greater detail below, and such as together form aprocess stream designated by the reference numeral 23, are appropriatelyprocessed through a compressor 24. The resulting compressed oxygenateconversion product stream 26 and, if desired, a recycle stream 30,described in greater detail below, and such as together form a processstream designated by the reference numeral 31, are introduced into anappropriate gas concentration system 32.

Gas concentration systems such as used for the processing of theproducts resulting from such oxygenate conversion processing are wellknown to those skilled in the art and do not generally form limitationson the broader practice of the invention as those skilled in the art andguided by the teachings herein provided will appreciate.

In the gas concentration system 32, the process stream 31 such asconstituting the compressed oxygenate conversion product stream 26 and,if used, the recycle stream 30, is processed to provide a fuel gasstream 34, an ethylene stream 36, a propylene stream 40 and a mixed C₄₊hydrocarbon stream 42, such as generally composed of butylene andheavier hydrocarbons.

The mixed C₄₊ hydrocarbon stream 42 is subjected to a fractionationsection 44 such as to form a purge stream 46 such as generallycomprising C₇₊ hydrocarbons and a process stream 50 such as generallycomprising C₄, C₅ and C₆ hydrocarbons. At least a portion of the processstream 50, e.g., the process stream portion 52, is introduced into anolefin cracking reactor section 54, such as in the form of a fixed bedreactor, as is known in the art and wherein the process stream portion52 contacts with an olefin cracking catalyst and at reaction conditions,in a manner as is known in the art, effective to convert C₄ and C₅olefins therein contained to a cracked olefins effluent stream 56comprising light olefins.

A purge stream 60 is shown whereby C₄-C₆ paraffin compounds and the likemay desirably be purged from the material stream being processed in thesystem 10, in a manner such as known in the art. As will be appreciatedby those skilled in the art and guided by the teachings herein provided,such compounds generally do not convert very well in olefin crackingreactors. Consequently, such purging can avoid the undesirable build-upof such compounds within the process system 10.

The cracked olefins effluent stream 56 is processed through a cooler 62to form a process stream 64. The process stream 64 is then processedthrough a gas-liquid separator 66 to form a recycle stream of gaseousmaterial, such as constituting the above-identified recycle stream 22and such as generally comprising C₁ and C₂ hydrocarbons. As shown, therecycle stream 22 can be combined with the oxygenate conversion productstream 16 and returned to the compressor 24. The gas-liquid separator 66also forms a process stream 70 such as constituting the remainder of thecracked olefins effluent such as generally comprising liquid materialand such as may be conveyed via a pump 72 such as to constitute therecycle stream 30, identified above, and such as for combination withthe compressed oxygenate conversion product stream 26 and subsequentprocessing through the gas concentration system 32. In accordance withthe illustrated embodiment, the recycle stream 30 can desirably beintroduced to the gas concentration system 32 without first undergoingcompression.

The system 10 desirably serves to increase or maximize the conversion ofthe oxygenate feedstock to light olefins while reducing or minimizingthe production of C₄₊ liquid. Further such an embodiment desirablyreduces or minimizes capital costs by utilizing a single or commoncompressor for the treatment of the effluent from the two reactorsections, i.e., the oxygenate conversion reactor and the olefin crackingreactor. Such embodiment still further reduces or minimizes capitalcosts by utilizing a single or common gas concentration system, such ascomposed of appropriate product fractionation and recovery sections, forthe treatment of the effluent from the two reactor sections.

FIG. 2 illustrates a system, generally designated by the referencenumeral 210, for the conversion of an oxygenate-containing feedstock toolefins in accordance with another embodiment. The system 210 isgenerally similar to the system 10 shown in FIG. 1 and described above.

More particularly, an oxygenate-containing feedstock 212 is introducedinto an oxygenate conversion reactor section 214 wherein theoxygenate-containing feedstock contacts with an oxygenate conversioncatalyst and at reaction conditions effective to convert theoxygenate-containing feedstock to an oxygenate conversion product streamcomprising fuel gas hydrocarbons, light olefins, and C₄₊ hydrocarbons,in a manner as is known in the art.

The oxygenate conversion reactor section 214 produces or results in anoxygenate conversion product stream 216 generally comprising fuel gashydrocarbons, light olefins, and C₄₊ hydrocarbons. The oxygenateconversion reactor section 214 may also, as shown, produce or result inwastewater stream 220, such as may be appropriately treated and disposedor recycled.

The oxygenate conversion product stream 216 and a recycle stream 222,such as described in greater detail below, and such as together form aprocess stream designated by the reference numeral 223, areappropriately processed through a compressor 224. The resultingcompressed oxygenate conversion product stream 226 and, if desired, arecycle stream 230, described in greater detail below, and such astogether form a process stream designated by the reference numeral 231,are introduced into an appropriate gas concentration system 232.

In the gas concentration system 232, the process stream 231 such asconstituting the compressed oxygenate conversion product stream 226 and,if used, the recycle stream 230, is processed to provide a fuel gasstream 234, an ethylene stream 236, a propylene stream 240 and a mixedC₄₊ hydrocarbon stream 242, such as generally composed of butylene andheavier hydrocarbons.

The mixed C₄₊ hydrocarbon stream 242 is subjected to a fractionationsection 244 such as to form a purge stream 246 such as generallycomprising C₇₊ hydrocarbons and a process stream 250 such as generallycomprising C₄, C₅ and C₆ hydrocarbons. At least a portion of the processstream 250, e.g., the process stream portion 252, is introduced into anolefin cracking reactor section 254, such as in the form of a fixed bedreactor, as is known in the art and wherein the process stream portion252 contacts with an olefin cracking catalyst and at reactionconditions, in a manner as is known in the art, effective to convert C₄and C₅ olefins therein contained to a cracked olefins effluent stream256 comprising light olefins.

Similar to the system 10 described above, a purge stream 260 is shownwhereby C₄-C₆ paraffin compounds and the like may desirably be purgedfrom the material stream being processed in the system 210, such as in amanner known in the art.

The cracked olefins effluent stream 256 is processed through a cooler262 to form a process stream 264. The process stream 264 is thenprocessed through a gas-liquid separator 266 to form a stream 268 ofgaseous material and a stream 270 such as constituting the remainder ofthe cracked olefins effluent such as generally comprising liquidmaterial and such as may be conveyed via a pump 272 such as toconstitute the recycle stream 230, identified above. As shown, therecycle stream 230 can desirably be introduced to the gas concentrationsystem 232 without first undergoing compression.

The system 210 primarily differs from the system 10, described above, bythe inclusion of an acid gas separation section 276. The acid gasseparation section 276 treats the stream 268 of gaseous material toremove acid gas therefrom such as may normally be present therein inrelatively minor or trace amounts. With such acid gas removal, a recyclestream of gaseous material is formed, such as constituting theabove-identified recycle stream 222 and such as generally comprising C₁and C₂ hydrocarbons. Such acid gas removal can be realized by variousmanners known in the art and can desirably occur prior to return of thematerial to the compressor 224. Such acid gas removal can significantlyfacilitate downstream material handling and permit the utilization lesscostly processing hardware. For example, through such acid gas removal,H₂S can desirably be kept out of the various process and product streamsand the need for the use of more expensive metallurgy in productcompressors and various downstream equipment can be minimized orpreferably avoided.

While embodiments utilizing a fixed bed olefin cracking reactor unithave been described above, those skilled in the art and guided by theteachings herein provided will appreciate that the broader practice ofthe invention is not necessarily so limited. To that end, reference isnow made to FIG. 3 which illustrates a system, generally designated bythe reference numeral 310, for the conversion of an oxygenate-containingfeedstock to olefins in accordance with yet another embodiment andwherein an olefin cracking reactor unit having the form of a moving bedreactor is utilized. The system 310 is generally similar to the system10 shown in FIG. 1 and described above.

More particularly, an oxygenate-containing feedstock 312 is introducedinto an oxygenate conversion reactor section 314 wherein theoxygenate-containing feedstock contacts with an oxygenate conversioncatalyst and at reaction conditions effective to convert theoxygenate-containing feedstock to an oxygenate conversion product streamcomprising fuel gas hydrocarbons, light olefins, and C₄₊ hydrocarbons,in a manner as is known in the art.

The oxygenate conversion reactor section 314 produces or results in anoxygenate conversion product stream 316 generally comprising fuel gashydrocarbons, light olefins, and C₄₊ hydrocarbons. The oxygenateconversion reactor section 314 may also, as shown, produce or result inwastewater stream 320, such as may be appropriately treated and disposedor recycled.

The oxygenate conversion product stream 316 and a recycle stream 322,such as described in greater detail below, and such as together form aprocess stream designated by the reference numeral 323, areappropriately processed through a compressor 324. The resultingcompressed oxygenate conversion product stream 326 and, if desired, arecycle stream 330, described in greater detail below, and such astogether form a process stream designated by the reference numeral 331,are introduced into an appropriate gas concentration system 332.

In the gas concentration system 332, the process stream 331 such asconstituting the compressed oxygenate conversion product stream 326 and,if used, the recycle stream 330, is processed to provide a fuel gasstream 334, an ethylene stream 336, a propylene stream 340 and a mixedC₄₊ hydrocarbon stream 342, such as generally composed of butylene andheavier hydrocarbons.

The mixed C₄₊ hydrocarbon stream 342 is subjected to a fractionationsection 344 such as to form a purge stream 346 such as generallycomprising C₇₊ hydrocarbons and a process stream 350 such as generallycomprising C₄, C₅ and C₆ hydrocarbons. At least a portion of the processstream 350, e.g., the process stream portion 352, is introduced into anolefin cracking reactor section 354 wherein the process stream portion352 contacts with an olefin cracking catalyst and at reactionconditions, in a manner as is known in the art, effective to convert C₄and C₅ olefins therein contained to a cracked olefins effluent stream356 comprising light olefins.

Similar to the system 110 described above, a purge stream 360 is shownwhereby C₄-C₆ paraffin compounds and the like may desirably be purgedfrom the material stream being processed in the system 310, such as in amanner known in the art, and such as to avoid the undesirable build-upof such compounds within the process system 310.

The cracked olefins effluent stream 356 is processed through a cooler362 to form a process stream 364. The process stream 364 is thenprocessed through a gas-liquid separator 366 to form a recycle stream ofgaseous material, such as constituting the above-identified recyclestream 322 and such as generally comprising C₁ and C₂ hydrocarbons. Thegas-liquid separator 366 also forms a process stream 370 such asconstituting the remainder of the cracked olefins effluent such asgenerally comprising liquid material and such as may be conveyed via apump 372 such as to constitute the recycle stream 330, identified above,and such as for combination with the compressed oxygenate conversionproduct stream 326 and subsequent processing through the gasconcentration system 332. As shown, the recycle stream 330 can desirablybe introduced to the gas concentration system 332 without firstundergoing compression.

The system 310 primarily differs from the system 10, described above, byrequiring that the olefin cracking reactor section 354 includes a movingbed reactor 390 which allows at least a portion of the catalyst from themoving bed reactor 390 to be regenerated on a continuous orsemi-continuous basis in a separate but integrated regeneration zone392.

The incorporation and use of moving bed (radial flow) reactor withcontinuous or semi-continuous catalyst regeneration for the cracking ofthe heavy recycle olefins can desirably serve to minimize the capitalcosts for the processing arrangement. For example, utilization of such amoving bed reactor with a continuous catalyst regenerator can desirablyallow the associated olefin cracking reactor to operate at a higheraverage conversion as compared to a typical swing bed reactor system. Inaddition, the reactor section effluent from such a moving bed reactordesirably provides or results in a steadier composition such as maydesirably simplify the design and operation of downstream fractionators.

If desired, the system 310 can be appropriately modified to incorporatean acid gas separation section (not shown), such as identified anddescribed above relative to the system 210, shown in FIG. 2.

While the invention has been described above making specific referenceto the processing of an oxygenate-containing feedstock comprising lightoxygenates such as one or more of methanol, ethanol, dimethyl ether,diethyl ether, or mixtures thereof, those skilled in the art and guidedby the teachings herein provided will appreciate that the broaderpractice of the invention is not necessarily so limited. Moreparticularly, suitable “oxygenate-containing” feedstocks employed in thepractice of the invention are to be understood to include alcohols,ethers and carbonyl compounds (aldehydes, ketones, carboxylic acids andthe like). Moreover, such suitable oxygenate-containing feedstockspreferably contain from 1 to about 10 carbon atoms and, more preferably,contains from 1 to about 4 carbon atoms. Suitable reactants includelower straight or branched chain alkanols, their unsaturatedcounterparts. Representatives of suitable oxygenate compounds include:methanol; dimethyl ether; ethanol; diethyl ether; methyl ethyl ether;formaldehyde; dimethyl ketone; acetic acid; and mixtures thereof.

Embodiments, such as described above, desirably provide or result inimproved processing of oxygenates to olefins, particularly such as toresult in an increase in the relative amount of light olefins, and whichprocessing is desirably more simple, effective, and/or economic thanheretofore reasonably possible. In accordance with particular suchembodiments, an oxygenate-containing feedstock can be converted to lightolefins in a catalytic reaction and heavier hydrocarbons (e.g., C₄₊hydrocarbons) formed during such processing can be subsequently crackedto increase the light olefins (e.g., C₂ and C₃ olefins) produced orresulting therefrom, with at least a portion of the oxygenate conversionproduct stream and at least a portion of the oxygenate conversionproduct stream being elevated in pressure, together or separately,through the same compressor prior to being routed through an appropriategas concentration system.

The invention illustratively disclosed herein suitably may be practicedin the absence of any element, part, step, component, or ingredientwhich is not specifically disclosed herein.

While in the foregoing detailed description this invention has beendescribed in relation to certain preferred embodiments thereof, and manydetails have been set forth for purposes of illustration, it will beapparent to those skilled in the art that the invention is susceptibleto additional embodiments and that certain of the details describedherein can be varied considerably without departing from the basicprinciples of the invention.

1. A process for producing light olefins from an oxygenate-containingfeedstock, said process comprising: contacting the oxygenate-containingfeedstock in an oxygenate conversion reactor with an oxygenateconversion catalyst and at reaction conditions effective to convert theoxygenate-containing feedstock to an oxygenate conversion product streamcomprising fuel gas hydrocarbons, light olefins, and C₄₊ hydrocarbons;compressing at least a portion of the oxygenate conversion productstream via a first compressor; treating the compressed oxygenateconversion product stream in a gas concentration system to recover lightolefins and to form a C₄₊ hydrocarbon stream; contacting at least aportion of the C₄₊ hydrocarbon stream in an olefin cracking reactor withan olefin cracking catalyst and at reaction conditions effective toconvert C₄ and C₅ olefins therein contained to a cracked olefinseffluent stream comprising light olefins; and returning at least aportion of the cracked olefins effluent stream to the first compressorfor combination with the oxygenate conversion product stream andsubsequent treatment in the gas concentration system.
 2. The process ofclaim 1 wherein the oxygenate conversion reactor is a fluidized bedreactor.
 3. The process of claim 1 wherein the olefin cracking reactoris a fixed bed reactor.
 4. The process of claim 1 wherein the olefincracking reactor is a moving bed reactor.
 5. The process of claim 4wherein the olefin cracking catalyst is continuously regenerated.
 6. Theprocess of claim 1 wherein the cracked olefins effluent stream isseparated into a first stream and a second stream, wherein the firststream is the portion returned to the first compressor for combinationwith the oxygenate conversion product stream and subsequent treatment inthe gas concentration system.
 7. The process of claim 6 wherein thesecond stream is introduced to the gas concentration system withoutcompression.
 8. The process of claim 6 additionally comprising treatingthe first stream to remove acid gas therefrom prior to return to thefirst compressor.
 9. The process of claim 1 wherein theoxygenate-containing feedstock consists essentially of methanol.
 10. Theprocess of claim 1 wherein subsequent to the treating of the compressedoxygenate conversion product stream, the process additionally comprisesfractionating the C₄₊ hydrocarbon stream to form a process streamcomprising C₄₊ through C⁶⁻ hydrocarbons and wherein the at least aportion of the C₄₊ hydrocarbon stream contacted with the olefin crackingcatalyst comprises at least a portion of the process stream comprisingC₄₊ through C⁶⁻ hydrocarbons.
 11. A process for producing light olefinsfrom a methanol-containing feedstock, said process comprising:contacting the methanol-containing feedstock in a methanol conversionreactor fluidized reaction zone with a methanol conversion catalyst andat reaction conditions effective to convert the methanol-containingfeedstock to a methanol conversion product stream comprising fuel gashydrocarbons, light olefins, and C₄₊ hydrocarbons; compressing at leasta portion of the methanol conversion product stream via a firstcompressor; treating the compressed methanol conversion product streamin a gas concentration system to recover light olefins and to form afuel gas hydrocarbon stream and a C₄₊ hydrocarbon stream; fractionatingthe C₄₊ hydrocarbon stream to form a process stream comprising C₄₊through C⁶⁻ hydrocarbons and a purge stream comprising C₇₊ hydrocarbons;contacting the process stream in an olefin cracking reactor with anolefin cracking catalyst and at reaction conditions effective to convertC₄ and C₅ olefins therein contained to a cracked olefins effluent streamcomprising light olefins; and separating the cracked olefins effluentstream into a first stream comprising C₁ and C₂ hydrocarbons and asecond stream comprising a remainder of the olefin cracking productstream, wherein the first stream is returned to the first compressor forcombination with the oxygenate conversion product stream and subsequenttreatment in the gas concentration system and the second stream isintroduced to the gas concentration system without compression.
 12. Theprocess of claim 11 wherein the olefin cracking reactor is a moving bedreactor.
 13. The process of claim 12 wherein the olefin crackingcatalyst is continuously regenerated.
 14. A system for convertingoxygenates to light olefins, said system comprising: a reactor forcontacting an oxygenate-containing feedstream with catalyst andconverting the oxygenate-containing feedstream to an oxygenateconversion product stream comprising fuel gas hydrocarbons, lightolefins, and C₄₊ hydrocarbons; a first compressor to compress at least aportion of the oxygenate conversion product stream to form a compressedoxygenate conversion product stream; a gas concentration system to treatthe compressed oxygenate conversion product stream to recover lightolefins and to form a C₄₊ hydrocarbon stream; a reactor for contactingat least a portion of the C₄₊ hydrocarbon stream with catalyst andconverting C₄ and C₅ olefins therein contained to a cracked olefineffluent stream comprising light olefins; and a first return linewherein at least a portion of the cracked olefin effluent stream isintroduced into the first compressor and subsequently processed throughthe gas concentration system.
 15. The system of claim 14 additionallycomprising: a cracked olefin effluent separation system effective toseparate the cracked olefin effluent into a first stream comprising C₁and C₂ hydrocarbons and a second stream comprising a remainder of thecracked olefin effluent; and a second return line wherein at least aportion of the second stream is introduced into the gas concentrationsystem without prior passage through the first compressor; wherein theportion of the cracked olefin effluent stream introduced into the firstcompressor and subsequently processed through the gas concentrationsystem comprises at least a portion of the first stream.
 16. The systemof claim 15 additionally comprising an acid gas neutralization reactordisposed between the cracked olefin effluent separation system and thefirst compressor, the acid gas neutralization reactor effective toneutralize acid gas present in the first stream prior to passage to thefirst compressor.
 17. The system of claim 14 wherein the olefin crackingreactor is a fixed bed reactor.
 18. The system of claim 14 wherein theolefin cracking reactor is a moving bed reactor.
 19. The system of claim18 additionally comprising a continuous catalyst regenerator wherein theolefin cracking catalyst is continuously regenerated.
 20. The system ofclaim 14 additionally comprising a fractionator to fractionate the C₄₊hydrocarbon stream to form a process stream comprising C₄₊ through C⁶⁻hydrocarbons and wherein the at least a portion of the C₄₊ hydrocarbonstream contacted with the catalyst in the reactor comprises at least aportion of the process stream comprising C₄₊ through C⁶⁻ hydrocarbons.